Compressor



Sept. 12, 1 R. E. WARREN ET AL COMPRESSOR Filed Aug. 8, 1957 u I l u I 2,999,630 COMPRESSOR Robert Evans Warren, Marblehead, Mass., and Felix Ernst Nagel, Columbus, and Gerhard Neumann and Le Var C. Jensen, Cincinnati, Ohio, assignors to General Electric Company, a corporation of New York Filed Aug. 8, 1957, Ser. No. 677,145 1 Claim. ((31. 230-114) This invention relates to an axial flow compressor for a turbojet engine which is provided with adjustable stator vanes, and, in particular, to a means for varying the position of several rows of stator vanes in the compressor of a turbojet engine.

More thrust can be obtained from a turbojet engine by providing a higher pressure ratio compressor for the engine. However, whenever a conventional compressor with fixed stator vanes is designed for high pressure ratio operation, stall characteristics occur during various part speed conditions. This is due to the fact that when a compressor is designed for a high speed, high pressure operating condition, the stator vanes are positioned at a particular angle of attack to give the most eflicient operation. However, at starting and part speed conditions, the angle of attack of the front rows of vanes will become mismatched from the vanes in the rear rows of the compressor so as to create stall. In other words, at the part speed condition, the rear stages cannot take the quantity of air that is being passed to it by the front stages. Accordingly, back pressure is built up so as to choke the compressor. In order to prevent this stall condition, adjustable stator vanes can be provided, so that at starting and part speed conditions the front stages can be closed down with respect to the rear stages and thereby provide the correct airfoil orientation angle for the particular velocity of flowing air. In this manner, a compressor having variable stator vanes overcomes the tendency of poor performance at the off design conditions when adjusting the angle of the stator vanes by rematching the characteristics of the front end stages with that of the back end stages of the compressor. The position of the stator vanes for various operating conditions can be scheduled as a function of engine speed, temperature and pressure. 7

Although many attempts have been made to vary the angles of attack of the rows of stator vanes simultaneously and in accordance with a predetermined schedule for various speeds of the engine, these attempts have failed in view of the various difiiculties of actuating the vanes. Previous attempts have been too cumbersome so as to destroy the purpose of achieving a light-weight, high pressure ratio single rotor compressor utilizing variable stator vanes. That is, the weight is increased to such an extent by previous mechanisms that the advantage gained is offset by the additional weight. Also, the vibrations occurring in the previous mechanisms are of such magnitude as to cause the various mechanical elements of the linkage mechanisms to fail. Further, the degree of accuracy of these mechanisms to control the angle of the stator vanes for satisfactory compressor operation has not been maintained. It is therefore an object of this invention to obviate the above difficulties and to provide a linkage mechanism for adjusting rows of stator vanes that will satisfy the requirements of relatively low weight, high strength, and accuracy of adjustment.

The best angle of attack for a particular row of stator vanes at various speed conditions may vary or be the same from row to row. Therefore, it is another object of this invention to provide a mechanical linkage arrangement that is capable of adjusting a row or rows of stator vanes through either the same, greater, or lesser angle than an adjacent or remote stage of stator vanes in Patented Sept. 1-2, 1961 order that the compressor operate efiioiently at 01f design conditions.

In the past, the adjustable rows of stator vanes have been provided with lever arms, the lever arms being interconnected by an actuating ring, with a means for simultaneously adjusting the rings. However, such a mechanical linkage arrangement is not adapted to fit into the space requirements of most aircraft gas turbines and still adjust the rows of vanes through the wide variations of angles from row to row. This is due to the relatively short length lever arms which are incapable of providing accurate angular movement to set the vanes of one row at their proper angle of attack with respect to the vanes of another row. The relatively large diiference in angle of travel from row to row is such that the previous means could not provide the accuracy with which to adjust the vanes. The lever arms themselves have been unable to accommodate these large differences of travel. In some instances the space limitations require that the actuator ring of one row be positioned in a direction forward of a row of vanes rather than rearward. The mechanical arrangement connected to such an actuating ring must be capable of adjusting the ring in an opposite direction, to adjust the vanes of that row in the same direction as the other rows. It is therefore another object of this invention to provide a mechanical linkage arrangement capable of adjusting the rows of vanes through relatively large different angles and to adjust the actuating rings in opposite directions from a single operating means.

One of the main difficulties encountered in the various variable stator arrangements has been in the bearing for the journal of a variable stator vane. If a ball or roller bearing arrangement is used between the casing and the journal of the variable stator vane, the ball or rollers of the bearing tend to gouge the races as a result of the vibration. Also, the compressor casing must be built up in this area to provide a bearing surface for these bearings. Ball, roller, or just plain journal bearings require lubricant and means to supply the lubricant to the wearing parts. The heat generated in this area tends to decompose the lubricant. In addition, air from the compressor leaks through the prior known bearing means for adjustably supporting the journals of the stator vanes. It is therefore another further object of this invention to supply a bearing for adjustably mounting a stator vane in a compressor casing which bearing requires no lubricant and acts as an air seal to prevent air ieakage from the compressor, in addition to having a low coefficient of friction.

In order to prevent the vibrations created in the com pressor from damaging the parts that go to make up the linkage mechanism for the variable stator, and in order to provide for the required accuracy of angular control of the vanes, the parts must be made to close dimensions and be tightly connected. When making the parts to close dimensions, various problems arise in making such a linkage arrangement operative. For example, one of the difficulties encountered is in the pivotal connection between the levers mounted on the stator vanes and the actuator ring. The pins in the openings of the actuator ring always tend to be directed in a radial direction, The openings in the levers tend to deviate from this radial direction causing the pin to either twist, or cause lever arms to twist. In other words, the actuator ring rotates in an arc of a circle and the lever arm in a plane tangent to this are of a circle so that binding of the parts will result.

It is therefore still a more specific object of this invention to provide a flexible connecting means between the actuating rings and lever arms for permitting the pin to remain in a radial direction without effecting the operation of the lever arms and still maintaining a close fit between these connecting parts.

Briefly stated, and in accordance with one aspect of this invention, a. mechanical linkage arrangement is provided for adjusting the stator vanes of an axial flow compressor which includes anti-friction means which requires no lubricant and acts as a seal, a flexible connection between the lever arms aud the actuating rings so as to eliminate a harmful binding condition, and a linkage arrangement which is adapted to actuate the actuating ring in opposite directions while still adjusting the stator vanes in the same direction.

These and other objects will become more apparent when read in the light of the accompanying drawings and specification wherein like parts have like numbers and wherein the parts are intended to be as generic in their application as the prior art will permit and wherein:

FIGURE 1 is a perspective view showing the actuating means on the outside of the compressor casing for actuating the variable stator vanes;

FIGURE 2 is a cross-sectional view taken on lines 2-2 of FIGURE 1 showing how the lever is connected to the actuator ring;

FIGURE 3 is a cross-sectional view taken on lines 3-3 of FIGURE 1 showing the stages of stator vanes and of the various sizes of lever arms;

FIGURE 4 is an enlarged view of a portion of FIG- URE 3 showing the mounting for the stator vane;

FIGURE 5 is a cross-sectional view taken on lines 5-5 of FIGURE 1 through the compressor casing showing the bellcrank and turn buckle arrangement;

FIGURE 6 is a view showing the fork clip and pin; and

FIGURE 7 is an enlarged view of the lever and actuator ring.

Referring to the figures, the numeral 10 generally designates a compressor casing that is capable of high pressure, high speed operation. The compressor casing is provided with a plurality of radial openings 12, each machined with a flat bearing surface 13 and corresponding to the number of adjustable stator vanes for each particular row or stage and for the number of adjustable rows or stages of vanes. It is noted that all of the rows of stages of vanes can be adjustable or only certain rows adjustable. Mounted in each of the openings 12 is a stator vane 14, connected to a circular support base member 16 in any well known manner such as brazing or welding. Also, the vane and vase can be forged as a single unit.

Although the following description will be made with respect to one stator vane, it is to be understood that the other vanes are constructed in the same manner. The support base member 16 is cylindrical in shape and is provided with a tang or a plurality of tangs 17 extending radially outward from the base member 16 in a direction opposite to the vane 14. The tangs are positioned in a predetermined relation with respect to the vane so as to give the proper angle of attack to the stator vane when the tangs are turned to a desired angular position. Mounted in the opening 12 in the compressor casing is a vane base journal 18 provided with a flat bearing surface 19. It is noted that the vane base journal 18 can be made as an integral part of the casing so as to reduce the number of parts required. In that event the flat bearing surface 19 would then form the bearing seat about opening 12. A collar or bearing cap 21 is positioned on the base support member and extends over the vane base journal 18. The collar or hearing cap 21 is provided with mating recesses or slots 22 so as to fit over the tangs 17. Positioned at each end of the vane base journal and about the circumference of the base support member 16 is sheet material 23 made of polytetraflouraethylene, a well known material. This sheet material separates the casing from the vane assemactuating band and while bly surfaces and not only acts as a seal but provides a dry lubricant surface therebetween. This material has a low coefiicient of friction, needs no lubricant, tends to dampen vibrations, and will not deteriorate under normal operating temperatures or vibratory forces. Further, it can be molded readily into irregular shapes to fit around the base of the stator vane and seat in the compressor casing.

Connected to the center of the support member 16 is a stud member 24. A vane lever arm 26 is mounted on the stud member 24 and is secured thereto by a nut or the like 28. The vane lever arm 26 also contains slots 29 to fit over the tangs 17. The slots 29 and tangs 17 fix the angular position of the vane lever arm with respect to the vane. This mounting arrangement secures the vane lever arm 26 to the base support member 16 of the variable stator vane so that the vane lever arm and the stator vanes move in unison.

The other end of the vane lever arm 26 is provided with an opening 30 so as to receive a rubber grommet assembly 32 or the like, which is fixedly secured therein. The rubber grommet assembly 32 contains an outer member 33 and a small cylindrical bronze or brass member 34, both bonded to a cylindrical rubber sleeve 35. The brass member 34 is adapted to receive the pin 36. The pin 36 has a head 37 thereon, the purpose of which will be more fully hereinafter explained. The rubber sleeve 35 permits twisting of the outer member 33 with respect to the cylindrical brass member 34 which remains in a radial direction. An actuator ring 38 for each stage of adjustable vanes extends circumferentially about the compressor casing and is coaxial therewith. An actuator ring 38 is pivotally connected to each row of vane lever arms 26 by the pin 36 extending through the rubber grommet 32. Since the actuator ring 38 is concentric with the axis of the compressor casing, the pins 36 in the actuator ring will always extend in a radial direction. The opening 30 in the lever arm 26 and outer member 35 will become misaligned with the pin 36 after adjustment from the zero or initial position of the stator vanes. This is due to the fact that the actuator ring moves in an arc of a circle and the lever arm in a plane tangent to the arc of the circle. The rubber grommet 32 will Permit the pin 36 to become misaligned with openings 30 and still permit the actuator ring and lever arms to operate satisfactorily.

In order to secure the pins 36 to the actuator band 38 the pins 36 are provided with circumferential slots or grooves 40 (FIGURE 6). A fork type spring clip 41 provided with circular notches 42 in the fork portion is adapted to be positioned in the groove 40 so as to retain the pin 36 in locking engagement with the actuator band 38 and the vane lever arm 26. This is accomplished by the arms 43 of the fork engaging the one side of the actuator ring and the groove of the pin 36 while the head 37 prevents movement in the other direction.

The number of actuator rings 38 are equal to the number of rows or stages of the variable stator vanes in the compressor. The actuator ring interconnects the lever arms of a row or stage so as to adjust them in unison.

In order to adjust the actuator rings 38 a turnbuckle arrangement 46 is pivotally connected to the actuator ring 38 and to bellcranks 48 at 50. There is one turnbuckle for each stage to provide independent movement of the actuator ring for that stage from the other stages if so desired. The pivotable connection at the turnbuckle includes a self-aligning bearing to prevent binding. This bearing can be a ball and socket arrangement or of the rubber grommet type as shown in FIGURE 2. A bellcrank 48 is pivotally mounted at its fulcrum on the compressor casing as shown at 52. There is one bellcrank for each row of stator vanes. The other end 54 of the bellcrank is attached to a common actuator rod 56.

Since small space requirements and various obstruc- 'the various operating conditions.

tions require a flexible mechanism that can operate the actuating rings in opposite directions, the mechanism as above described can meet these requirements. The inlet guide vanes at 58 are generally mounted in a front frame and connected to the compressor frame through bolted flanges. The inlet guide vanes shovm at 58 are provided with lever arms which are connected to one of the actuator rings 38, which in turn is connected, through a bellcrank 62, to the common actuator rod 56. This arrangement turns the inlet guide vanes in unison with the other variable stator vanes. However, in view of the obstructions and space requirements the bellcrank 62 is reversed from the other bellcranks 48 so as to actuate the actuating rings 38 in a direction opposite to the others. The lever arms on the guide vanes are also reversed. Thus, even though the actuator ring is rotated in the opposite direction from the others, the inlet guide vanes 58 are rotated in the same direction as the others.

It is noted that the length of the lever arms for each stage, and the distances between the pivot points at 50 and 52 on the bellcranks are critical since they vary with different stages in order to give varying amounts of turning movement to the stator vanes of each adjustable stage so as to provide the best angle of attack for the particular operating condition. Use is made of both the lever arm length distance and the distance between the pivot points 50 and 52 to achieve wide variation but accurate adjustment of the rows of stator vanes. In view of the small space consideration and accuracy requirement, adjusting only the lever arms directly has proved to be unsatisfactory. The addition of the bellcranks provide the necessary flexibility to the linkage to overcome the space limitation and meet the accuracy requirement. The dimensions of the lever arms and bellcranks are made in accordance with a predetermined schedule to provide the best angle of attack of the stator vanes for The actuator rod 56 is shown connected to a cylinder 64 which can be either hydraulically or electrically operated. This actuator arrangement for actuating the stator vanes may be automatically operated in response to speed, temperature, or pressure signals measured at the various locations in or outside of the engine.

As pointed out previously, axial flow compressors for turbojet engines have aerodynamic characteristics which vary over a wide range. Some stages of stator vanes may require adjustment through a large angle of travel while others merely require a small angle of travel. However, the space requirements are such that the lever arms might be too small or too large to provide the required accurate aerodynamic adjustment to the stator vanes. The lever arms 26 are not capable of providing the necessary adjustment nor the accuracy required. Accordingly, the bellcranks 48 provide the additional means necessary to adjust the stator vanes so that they can meet the aerodynamic requirements. For example, reference is made to FIGURE 1 in which the lever arms 62 for the inlet guide vanes at 58 are much smaller than the lever arms for some of the other stages of vanes, due to a lack of space. If the aerodynamics require that the inlet guide vanes be adjusted equally with the other stages, and if the lever arms are the only mechanical means for adjusting the vanes, then the aerodynamic requirements could not be met. However, by the use of the bellcranks, the inlet guide vanes can be adjusted equally with the other stages by making the length between points 69 and 63 on the bellcrank smaller by a similar amount.

By this arrangement, any desired angle of adjustment can be provided to any of the stages of stator vanes. For example, some or all can be adjusted equally, or some can be adjusted equally while other stages are adjusted unequally over a wide range. In some cases, the aerodynamics may even require the vanes of a stage to be 6 turned in an opposite direction to the other stages. This can also be accomplished with this arrangement.

Also, as pointed out above, the mechanism for adjusting the inlet guide vanes cannot norrnallly be fitted in the limited space so that the lever arms for the inlet guide vanes are placed on the opposite side from the other lever arms. Therefore, the actuator ring is turned in an opposite direction. This movement in a direction is counteracted by placing the fulcrum 60' of the bellcrank 62 to the right of the pivot point at 63 whereas in the other bellcranks 48 the fulcrum 52 is to the left of the pivot point at 50. Further, if it is desired to adjust all the stages equally, and due to space considertions the lever arms cannot be of the same length, the distance between the pivot points 50 and 52 and 60 and 63 of the bellcranks can be dimensioned in order to make up the difference in length of lever arms and thereby still actuate the stator vanes through the same angle.

In operation, as the engine increases its speed the actuator piston and cylinder arrangement 64 automatically changes the position of the actuating rod 56 and of the bellcranks 48 which in turn actuate the actuator rings 38. Movement of the actuator rings 38 is transmitted to the vane levers 26 through the pins 36. It is noted that as the actuator rings 38 travel circumferentially about the compressor casing, the pins 36 tend to twist the rubber sleeve 35. The rubber grommet 32 permits this twisting to take place without disrupting the operation of the device. Since the actuator rings 38 are supported by the vane lever arms 26, the actuator rings 38 will move in an axial direction as well as in a circumferential direction. Also, the levers 26 have a high degree of stiffness so as to minimize the flexing of the actuator rings.

The purpose of the fork clip 41 is to make it possible to secure the pin 36 in place. Insuflicient space between the actuator band and compressor casing prevents the insertion of a normal bolt and nut or the like. Further, it is desirable that the pin head 37 be flush with the outside of the actuator band. Therefore, the head 37 is positioned in a counter bore as shown in the actuator ring. Also, the pin is so small that threads, or an opening through it, becomes difficult to fabricate and put together. Therefore, the fork clip provides a novel means of retaining a pin in place where size, space and accessibility become important criteria.

It is significant to note that the flat sheet material 23 made of polytetrafluoraethylene serves to function not only as a low friction bearing material between the compressor casing and the base of the stator vanes, but also as a seal to prevent air leakage from the comperssor casing and as a dry lubricant.

The use of flat material allows the base of the stator vianes to be supported on a fiat machined bearing surface on the comperssor casing in a direction perpendicular to the radius of the casing instead of only in a radial direction. This eliminates the necessity of building up the casing at the vane base openings.

The variable stator mechanism is used in such a manner as to control the compresser airflow, thereby making possible the operation of a high pressure ratio compressor with good fuel economy at low Mach numbers even though it is designed for operation at high Mach num-' bers. In addition, the flexibility of the variable stator mechanism allows high air flows at high Mach numbers, thus increasing the available thrust at the high Mach number condition. This variable stator design permits the construction of a simple single rotor compressor compatible with the lightweight design objectives of an aircraft turbojet engine.

While a particular embodiment of the invention has been illustrated and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention, and it is intended to cover in the appended claim all such spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

A compressor for an axial flow machine comprising: a casing having an inlet and an'outlet; a series of guide vanes adjustably mounted in a row in the inlet of said casing; a plurality of rows of stator vanes adjustably mounted in said casing doWntrearn of said row of guide vanes; a plurality of rows of lever arms, the lever arms of one row being connected to said inlet guide vanes and the arms of the remaining rows being connected to said stator vanes; a plurality of actuator rings, the lever arms of each of said plurality of rows being connected to one of said rings; the actuator ring for said row of guide vanes .being positioned on the downstream side of the associated guide vanes and the actuator rings for said rows of stator vanes being positioned on the upstream side of the associated stator vanes; a plurality of bellcranks pivotally mounted on said casing, each bellcrank being connected at one of its ends to one of said plurality of actuator rings and at its other end to a common actuator arm, the bellcrank connected to the actuator ring of said one row of lever arms of said guide vanes being reversed from the bellcranks connected to said remaining rows of lever arms, the remaining rows of lever arms also being reversed from said one row, in order that the actuator ring connected to said one row of lever arms may be turned in a direction opposite to the actuator rings of said remaining rows to turn all of the vanes in the same direction.

References Cited in the file of this patent UNITED STATES PATENTS 1,907,506 Coburn May 9, 1933 2,371,706 Planiol Mar. 20, 1945 2,651,492 Feilden Sept. 8, 1953 2,814,430 Beckett Nov. 26, 1957 2,842,305 Eckenfels et al. July 8, 1958 2,858,062 Allen Oct. 28, 1958 FOREIGN PATENTS 754,335 Great Britain Aug. 8, 1956 

